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OCCULTATION OF UCAC4_579-041439 BY 1089 Tama
2014 February 23

A 1.36 second occultation was recorded by Brian Loader, using video OSD technique.

Sadly there were 5 other observers registered for this event but cloud or gale prevented them observing so no clearly observed misses were recorded for this event.

View the TT14 prediction.

  1    B Loader, Darfield,NZ
  2(P) Prediction, TT14 Jan 30


Tama occultation - 2014 February 23


The circle above is plotted at the expected 13 km diameter of Tama. With only one chord it is not possible to determine whether Brian was north or south of the central line of the event.

The figure below shows the Limovie/Tangra light curve of the occultation.

Tama occultation - 2014 February 23

There are small problems with this observation.

- The dip while very clear is only 2 sample periods long. We normally ask for at least 3 samples at the bottom to feel sure of an event.

-The predicted line does not show on the plot. Tama is small at 13 km so it should not surprise us with a rank of only 13 that it could be out of the picture even at minimum zoom. If the observation and prediction were close we might feel more confident that the dip was real and not "just noise"

- There are other single sample noise dips of similar magnitude visible in all 4 stars measured.

We should therefore be wary of using this result for astrometry.

I put these issues to Brian and his reply is:

I had, of course, one advantage in that I watched the appulse on the monitor and "saw" the event clearly. At 16x integration it lasted well over 1 second.
Perhaps a couple of points that should be mentioned? The drop in the light curve is close to that expected, delta mag 1.4 or 72%.
Tama is shown by Occult as having a satellite or, possibly more correctly, as a double asteroid with the "satellite" diameter given as 9km. So any event could have been due to the satellite. But the separation is shown as only 20 km, so that wouldn't bring the event significantly closer.


When we add those fators we may feel the probability is higher that this was "real", but any astrometry report should probably qualify the result as "uncertain"

Observational Data:

Observation details for MP ( 1089 ) Tama
By Star              UCAC4 579-041439
On 2014-02-23  at 10:38:14.0


Observer   B. Loader
Location   Darfield,NZ
Longitude  +172:06
Latitude   -43:28
Altitude   210 m
Datum      WGS84
Telescope SCT including Cass and Mak
Aperture   25 cm
Seeing     Slight flickering Clear
Camera Type  WAT120N+       PAL/CCIR
Camera Delay -0.35
Timing     GPS - time inserted Video with frame analysis
Disappearance  10:38:23.40
Reappearance   10:38:24.76
Comments: Event recorded using OccuRec.  Clear event for 2+ integrated frames.
Times and accuracy determined by visual examination of Tangra light curve.
Report prepopulated by IOTA Reporting Add-in for OW ver.1.8


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